Anesthesia and analgesia
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Anesthesia and analgesia · Jan 2003
Case ReportsCompression of the pulmonary artery during transesophageal echocardiography in a pediatric cardiac patient.
Hemodynamic compromise caused by the insertion of the probe for transesophageal echocardiography in a patient with severe stenosis of the main pulmonary artery is reported for the first time. The first symptom of the impending problem was a rapid decrease of end-tidal CO(2).
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Anesthesia and analgesia · Jan 2003
Volatile anesthetics reduce agonist affinity at nicotinic acetylcholine receptors in the brain.
In previous studies we and others have demonstrated that the activation of nicotinic acetylcholine receptors (nAChRs) is inhibited by subanesthetic concentrations of volatile anesthetics. The mechanism by which activation is inhibited is unknown. Studies of the evolutionarily related nAChRs from the electric fish Torpedo have suggested that volatile anesthetics alter the affinity of the agonist for the receptor. We studied the effect of two volatile anesthetics, isoflurane and sevoflurane, on equilibrium binding of the high-affinity nicotinic agonist epibatidine to nicotinic receptors from mouse brain. We studied binding to male and female brain separately, because sex differences in nicotine responses have been reported. Male and female brains have equal epibatidine binding without anesthetic. Isoflurane and sevoflurane reduce the binding of [(3)H]epibatidine to male and female nicotinic receptors, but only at concentrations at and above those required for anesthesia. The 50% inhibitory concentration for isoflurane inhibition of [(3)H]epibatidine binding to male brain was 0.58 +/- 0.07 mM and to female brain was 1.62 +/- 0.30 mM. The 50% inhibitory concentration for sevoflurane inhibition of [(3)H]epibatidine binding to male brain was 0.77 +/- 0.05 mM and to female brain was 0.77 +/- 0.04 mM. There was no statistically significant difference in the effect of either drug between sexes (P > 0.05). Although there is a slight decrease in agonist affinity at anesthetic concentrations, the marked reductions in nAChR function at subanesthetic concentrations cannot be attributed to changes in agonist affinity. ⋯ Volatile anesthetics reduce the activation of nicotinic acetylcholine receptors by an unknown mechanism. We have demonstrated that although isoflurane and sevoflurane inhibit agonist affinity, the concentrations required are too large to be responsible for the dynamic changes observed.
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Anesthesia and analgesia · Jan 2003
Extending the skeletal muscle viability period in the malignant hyperthermia test.
The caffeine halothane contracture test (CHCT) is the only validated test for diagnosing malignant hyperthermia (MH) susceptibility (MHS) and phenotyping MHS families. Although most diagnostic laboratory tests can check intra- and interlaboratory consistency through the use of standard control samples, there has been no practical way to achieve this goal for the CHCT. The distances between diagnostic centers and time constraints of the CHCT protocol (5 h) prohibit centers from sharing tissue samples. In this study, we investigated varying storage conditions to extend the standard viability period of skeletal muscle to 24 h. Twenty MHS patients were tested according to the North America protocol. After standard CHCT, the surplus muscle samples were placed in one of the following four treatment groups. In Groups 1 and 2, muscles remained under tension and were stored in Krebs buffer (pH 7.4) at 23 degrees C-25 degrees C (clamped-warm) and 4 degrees C (clamped-cold), respectively. In Groups 3 and 4, muscle strips were dissected, and the ends were tied with silk sutures, cut from the clamp, and placed in Krebs buffer at 23 degrees C-25 degrees C (free-warm) and 4 degrees C (free-cold), respectively. The responses of the treatment groups to halothane (3%) and caffeine (0.5-32 mM) were tested at 22-26 h after excision. The clamped-warm storage group correctly diagnosed MHS in all patients. ⋯ Varying conditions for storage of muscle were investigated to extend the viability period of muscle in the malignant hyperthermia (MH) test from 5 to 24 h. Muscles stored for 24 h under tension at room temperature remained viable and correctly diagnosed MH susceptibility in all patients.
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Anesthesia and analgesia · Jan 2003
Minimum alveolar anesthetic concentration of isoflurane with different xenon concentrations in Swine.
For patients requiring a fraction of inspired oxygen more than 0.3, the use of xenon (Xe) as the sole anesthetic is limited because of its large minimum alveolar anesthetic concentration (MAC) of 71%. This warrants investigating the combination of Xe with other inhaled anesthetics. We therefore investigated the influence of Xe on the MAC of isoflurane. The study was performed in 10 swine (weight, 28-35 kg) ventilated with Xe 0%, 15%, 30%, 40%, 50%, and 65% in oxygen. For each Xe concentration, various concentrations of isoflurane were administered in a step-wise design. For each combination, a supramaximal pain stimulus (claw-clamp) was applied, and the appearance of a withdrawal reaction was recorded. The isoflurane MAC was defined as the end-tidal concentration required to produce a 50% response rate. At each Xe concentration, the responses to the pain stimulus were categorized, and a logistic regression model was fitted to the results to determine isoflurane MAC. Isoflurane MAC was decreased by inhalation of Xe in a nonlinear manner from 1.92% (95% confidence interval, 1.70%-2.15%) with 0% Xe to 1.17% (95% confidence interval, 0.75%-1.59%) with 65% Xe. Although this indicates partial antagonism of the two anesthetics, a combination of Xe with isoflurane may prove valuable for patients requiring a fraction of inspired oxygen more than 0.3. ⋯ We investigated the influence of the anesthetic gas xenon on the minimum alveolar anesthetic concentration (MAC) for isoflurane (another anesthetic gas). The study was performed in 10 swine ventilated with fixed xenon and various concentrations of isoflurane. The isoflurane MAC is decreased by inhalation of xenon in a nonlinear relationship.
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Anesthesia and analgesia · Jan 2003
Neurologic complications of 405 consecutive continuous axillary catheters.
Continuous axillary brachial plexus block may theoretically increase the risk of neurologic complications because of catheter-induced mechanical trauma or local anesthetic toxicity. In this study, we retrospectively reviewed the frequency of complications using current techniques and applications. There were 405 continuous axillary catheters in 368 patients. A preexisting neurologic condition was present in 41 (10.1%) patients, including 30 patients with a preoperative ulnar neuropathy. In 305 (75.3%) cases, the axillary catheter was placed to facilitate rehabilitation after major elbow surgery. Catheters were typically placed postoperatively, after documentation of the patient's normal neurologic examination. The local anesthetic infusion contained bupivacaine in 355 (88.7%) patients and mepivacaine in 45 (11.1%) patients. The mean infusion rate was 10 +/- 2 mL/h. Catheters remained indwelling for 55 +/- 32 h. In 31 patients, the axillary catheter was replaced because of technical problems or inadequate analgesia. There were 9 complications in 8 patients for an overall frequency of 2.2%. Complications included one each of the following: localized infection (treated with catheter removal and antibiotics), axillary hematoma, and retained catheter fragment requiring surgical excision. In addition, two patients reported signs and symptoms of systemic (preseizure) local anesthetic toxicity. Four (1.0%) patients reported new neurologic deficits postoperatively. In two patients, the neural dysfunction was non-anesthesia related. All four had continuous catheters placed after major elbow surgery. We conclude that the risk of neurologic complications associated with continuous axillary blockade is similar to that of single-dose techniques. ⋯ We evaluated the risk of neurologic complications in 368 patients undergoing 405 consecutive continuous axillary blocks. New neurologic deficits were reported in four patients. This series suggests that the risk of neurologic complications associated with continuous axillary block is similar to that of single-dose techniques.